I guess you were meaning to say that they are under the new covenant. So, they have not obligation to obey the law.
We are not saved by obeying the law. We are saved by grace through believing in Him. But a sign that someone truly believes is that they will leave their sin. 2Tim 2:19 says "All who belong to the Lord must turn away from evil."
Stopping sin is a result of real belief, and remorse and contrition. God desires a broken and contrite heart.
If I was to hit you and then say sorry, you would accept my apology. Then if I was to hit you the following day and then say sorry, you would begin to wonder if I was truly sorry. Then the day after this, I did the same thing, you would realise that I was not truly sorry. My words may say one thing, but my actions show another. What you act out is what you truly believe. If you are truly broken and contrite because you have sinned against God, then there will be a change in you. That is why the bible says that we are given a new heart and new mind. One that obeys Him. "I will give you a new heart and a new mind. I will take away your stubborn heart of stone and give you an obedient heart." Eze 36:26
Belief by itself will not save you. Even the demons believe.
Yes, we should also help with discipling a new believer if possible. But in many instances, we may not have the opportunity. Just like with when Philip spoke to the Ethiopian eunuch in his chariot. It says that Philip no longer saw him. So, there are times when we must trust that if God starts a work in someone, then He will complete it.
Jesus did not have time to disciple all the 5000 people that he fed.
So, I am not discounting relationships. They are good. But we need to make sure that we put the proclamation of the Gospel over friendship evangelism.
I don't talk about repentance first and then give someone the Gospel. I tell them about repentance once I have given them the Gospel.
But I do give them the law first. So, I show them their sins and then I tell them that one day God will judge everyone. This creates a fear of God in them and in Proverbs 9:10 it says, "The fear of the Lord is the beginning of wisdom." And in Psalms 19:7 it says, "The law of the LORD
is perfect, converting the soul; The testimony of the LORD
is sure, making wise the simple;"
It is a bit like if a doctor just gave someone medicine (the Gospel) and said to take this medicine without giving any reason. The person receiving it would not take it as they believe they are fine. But if you show a person their x-rays (using the law) and show them the symptoms, and you tell them the serious consequences of not taking the medicine, then they will jump at the chance to take the medicine.
Also, if we do not use the law, then we can make weak believers. When persecution comes, they can fall away easily. But if someone has seen their sin truly for what it is, and they know that God will judge them one day, then when persecution comes, they will be less likely to fall away, because they know of the seriousness if they do. Proverbs 16:16 says, By the fear of the Lord, one departs from evil." And that fear will make you realise that you do not want to go against God. So, that fear is good. It is your friend.
If the law is preached first, it will help to make strong believers. They will not shrink back when times get hard.
A parable. Mark 4:16-17 says "And in a similar way these are the ones sown
with seed on the rocky
places, who, when they hear the word, immediately receive it with joy; and
yet they have no
firm root in themselves, but are
only temporary; then, when affliction or persecution occurs because of the word, immediately they fall away. "
If someone is shown their sin, they will have a broken and contrite heart. They will most likely even have tears because they have seen how they have dishonoured God and they have seen how big the sacrifice was that was done for them. But someone who has only been given the Good News without the bad news, will be filled with joy when they believe. Much like in this parable. Who would not be happy if all they were told is good stuff, like you are going to heaven? But in these people the root is weak, and they can shrink back once persecution happens. Because persecution is not like the blessing that they had been promised. So, the law helps to make a strong root.
Also just saw a new vid that has come out and it mentions about putting the law first. It mentions it at the start and then just after halfway it gets back into it. So, watch the whole thing. It is really interesting. Even the other stuff that is not related to this thread.